The American implementation of unions, on the other hand, is not great. While in the US, I've run into rules like not being allowed to plug something in because only union electricians are allowed to do that, and that's just one example among many. Police unions and teacher's unions are mostly known for making bad employees unfirable outside of egregious circumstances, and teacher's unions in particular don't seem to have improved pay or working conditions much.
I have no idea where the difference comes from, but for people who have only seen and interacted with the American system, I don't blame them for not liking unions